The microstructural evolution and grain-boundary influence on electrical properties of Ce0.90Gd0.10O1.95 were studied. the nanoscale powders synthesized from a semibatch reactor exhibited 50% green density and 92% sintering density at 1200°C (∼200°C lower than previous studies). Impedance spectra as a function of temperature and grain size were analyzed. the Ce0.90Gd0.10O1.95 with finest grain size possessed highest overall grain-boundary resistance; this contribution was eliminated at temperatures >600°C, regardless of grain size. the grain conductivity was independent of grain size and was dependent on temperature with two distinct regimes, indicative of the presence of Gd′Ce−Vo∘∘ complexes that dissociated at a critical temperature of ∼580°C. the activation energy for complex dissociation was ∼0.1 eV; the value for the grain-boundary was ∼1.2eV, which was size independent.